Planar Array Contact Memory Cards

ABSTRACT

A Planar Memory Module (PAMM) device comprising a generally planar card comprising a first side and a second side, the first side having a plurality of couplings and the second side having a plurality of connectors, a plurality of memory devices coupled to the card via a first portion of the plurality of couplings, and at least one hub chip coupled to the card via a second portion of the plurality of couplings. Each of the plurality of couplings is connected to an associated one of the plurality of connectors.

This Invention was made with Government support under prime contractH98230-04-C-0920 awarded by the Maryland Procurement Office (MPO). TheGovernment has certain rights in this invention.

FIELD OF THE INVENTION

This invention relates generally to a system for packaging memorydevices for electronic computer systems.

BACKGROUND OF THE INVENTION

Electronic computing machines make common use of dual inline memorymodules (DIMMs). In particular, memory DIMMs which adhere to an industrystandard, or which are customized, are widely used to provide memorycapability to electronic computing devices. In a common configuration, aDIMM is a circuit card incorporating multiple dynamic random-accessmemory (DRAM) devices and, optionally, circuitry for clock, address, andcontrol distribution, as well as possible data re-buffering, errorcorrection, and serialization. Typically, each DIMM is attached to asystem planar via a memory connector. As used herein, “system planar”refers to any and all generally planar system components of anelectronic computing device capable of sending and receiving digitaldata.

Unfortunately, such a configuration is not optimal in situations whichrequire high-speed memory operations between the circuitry of the systemplanar and the memory and other circuitry on the DIMM. In the particularcase of high-speed memory access, all clock, address, and control data,as well as data passed to and from the DIMM, must pass through thememory connector. The memory connector is physically large, limited inthe number of connector pins contained thereupon, and is usuallyattached to the system planar through pins either soldered or press-fit.As the physical size of DRAMs continues to decrease, the memoryconnector increasingly functions as a bottleneck slowing the movement ofdata between the electronic computing device and the DIMM.

In addition to the diminution in the speed of data transfer, thepresence of the connector creates additional problems. The connectorpins are physically large and result in relatively large holes in theplanar that can block wiring channels. Soldering the connector pins isan environmental hazard, and can also cause deflection of the DIMMmaking the attachment of other components difficult. Connectors cannotbe easily placed back-to-back, on opposite sides of a circuit board, asthe connector pins occupy nearly all the space between adjacentconnectors. In addition, each connector is an impedance discontinuity tohigh-speed signaling and often requires that a ground return be placedimmediately adjacent to the connector in order to reduce undesiredreflections and cross talk to other signal lines.

Connectors suitable for packaging of dense electronics, such as those inso called “blade” servers and laptop computers typically place the DIMMat right angles to the system planar. A DIMM that is situated at a rightangle to the system planar is prone to becoming dislodged from theconnector, especially during shipping. While the incidence ofdislodgement can be ameliorated through the use of latching mechanisms,such mechanisms tend to block airflow and add cost to the design.Furthermore, DIMM connectors can be unreliable as they are“single-wipe”, metal-on-metal contacts and thus are subject to corrosivefailures.

Meanwhile, the other end of a DIMM memory net is typically either anindependent memory controller or a memory controller integrated into acomputer processor chip. The processor chip is often mounted on arelatively low-cost plastic first-level package. Such plastic packagestake the densely spaced signal and power connections of the processor orcontroller and “fan-out” to a coarser array of contacts. The packagedprocessor chip is often then connected in turn to a circuit boardthrough an array connector; an example of which might be a low-cost,reliable, land-grid-array connector although any array based (co-planar)connector will suffice.

Attempts to improve the DIMM form factor have focused primarily on thebenefits of miniaturization. However, smaller DIMMs tend to cause amyriad of alignment and reliability problems. Alternatively, slantingthe DIMM towards the system planar tends to degrade electricalperformance. While surface mount techniques might appear to be useful,surface mount DIMM connectors are difficult to solder given it's longand narrow aspect ratio.

What is needed is a device for coupling integrated circuits, such asmemory devices, to a system planar that does not exhibit theshortcomings known in the art.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the invention, a memory modulecomprises a generally planar card comprising a first side and a secondside, said first side comprising a plurality of couplings and saidsecond side comprising a plurality of connectors, a plurality of memorydevices coupled to said card via a first portion of said plurality ofcouplings, and at least one hub chip coupled to said card via a secondportion of said plurality of couplings wherein individual ones of saidplurality of couplings are connected to other ones of said plurality ofcouplings and other ones of said plurality of connectors via a pluralityof internal connectors.

In accordance with a further embodiment of the invention, a methodcomprises providing a generally planar card comprising a first side anda second side, the first side comprising a plurality of couplings andthe second side comprising a plurality of connectors; coupling aplurality of memory devices attached to the first side of the card to atleast one memory hub also attached to the first side of the card via afirst portion of the plurality of couplings, and coupling at least onehub chip via a second portion of the plurality of couplings to anassociated plurality of connectors on the second side of the card.

In accordance with another embodiment of the invention, an apparatuscomprises a system planar and a card coupled to the system planar. Thecard comprises a first side and a second side, where the first sidecomprises a plurality of couplings and the second side comprises aplurality of connectors. There are a plurality of memory devices coupledto the card via a first portion of the plurality of couplings, and atleast one hub chip coupled to the card via a second portion of theplurality of couplings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is an illustration of an embodiment of a top side of the PlanarMemory Module (PAMM) of the invention.

FIG. 1 b is an illustration of an embodiment of a bottom side of thePAMM of the invention.

FIG. 2 a is a schematic diagram of the system planar wiring for anembodiment of a PAMM.

FIG. 2 b is a diagram of the connectors of an embodiment of a PAMM.

FIG. 3 a is an illustration of an embodiment of a top side of the PAMMof the invention.

FIG. 3 b is an illustration of an embodiment of a bottom side of thePAMM of the invention.

FIG. 4 is a detailed schematic diagram of the wiring for the PAMM ofFIG. 3 b.

FIG. 5 a is an illustration of an embodiment of a top side of the PAMMof the invention.

FIG. 5 b is an illustration of an embodiment of a bottom side of thePAMM of the invention.

FIG. 6 is a perspective illustration of an embodiment of a PAMM coupledto a system planar.

FIG. 7 is a perspective illustration of a heatsink coupled to a PAMM.

FIG. 8 is a perspective illustration of the means for attaching aheatsink to a PAMM.

FIG. 9 a is a cross section illustration of a PAMM.

FIG. 9 b is a cross-section illustration of a PAMM wherein DRAMs areattached to two sides of the PAMM.

FIG. 10 is a perspective illustration of the PAMM of FIG. 9 b.

DETAILED DESCRIPTION OF THE INVENTION

In an embodiment of the invention, a planar memory module (PAMM) isprovided. Each PAMM is formed from a generally planar card coupled via afirst surface to at least one memory device and is capable of beingcoupled via a second side to the system planar. The PAMM card may becoupled to the system planar via an array connector such as a land gridarray (LGA) interposer, an FCI Connect Megarray, and and Intel pingridarray. As a result, co-planar array connector technology and laminatefirst level package technology, such as that used for processors, iscombined to address the particular requirements of memory utilizationfor electronic computing devices.

With reference to FIGS. 1 a and 1 b, there is illustrated a PAMM 10 andopposing sides of an embodiment of a PAMM card 11 coupled to multiplememory devices 13 and a single hub chip 15. Hub chip 15 operates tosynchronize and control the flow of digital data amongst the multiplememory devices 13 and between the PAMM 10 and the system planar. The hubchip can provide a variety of functions. Some functions which havealready become standard in the industry, or poised to become high-volumestandards are as follow. First, the hub chip 15 distributes clocksignals and re-buffers the address and control functions to the DRAMs sothat the memory controller need only control the state of the hub chipinputs, while the hub chips 15 output then change the state of the DRAMclock, address, and control inputs. Alternatively, the hub chip 15 canre-buffer the data thereby completing the standard for the JEDEC “fullybuffered DIMM”, or FBDIMM. In such a case the hub chip 15 serializes thedata stream to and from the DRAM, and communicates to the memorycontroller at a faster speed, through fewer signals, than the DRAM bus.Other hub-chip functions include performing high-level functionsnormally found in a memory controller.

FIG. 1 a shows a top side of the PAMM card 11. As used herein, “top”refers to a side of the PAMM card which faces away from the systemplanar when the PAMM 10 is secured to the system planar. Conversely, the“bottom” side of PAMM card illustrated in FIG. 1 b refers to the side ofthe PAMM card that is mounted facing the system planar. PAMM 10 is shownin exemplary fashion with nine memory devices 13, preferably DRAM chips,and a single hub chip 15 coupled to the top side of PAMM card 11. Feweror more DRAMs can be accommodated. The bottom side of PAMM card 11 isillustrated with an exemplary number of one hundred and ninety-twoconnectors 17, 23, 25. Each connector 17, 23, 25 is an electricallyconductive structure, including, but not limited to, a pin or a tab,capable of coupling with an associated structure on the system planar.Such a coupling may be accomplished through direct contact (e.g. directsoldered), or preferably, as described below, via a co-planar arrayconnector. Examples of array connectors include, but are not limited to,an LGA interposer with retention, and a two-piece separable arrayconnector of which several examples are known in the art.

With reference to FIG. 2 a, there is illustrated in schematic fashion anembodiment of a portion of the system-planar wiring 24 on the systemplanar (not shown) overlaid on the connectors 17, 23, 25 arranged on thebottom side of the PAMM card 11. Each connector is either a signalconnector 17, a power connector 25, or a ground connector 23. Powerconnectors include, but are not limited to, voltage pins supplyingdifferent voltages, and pins supplying a reference voltage as opposed tosourcing current. A signal connector 17 may be coupled to a single wireof the system planar wiring 24 over which is transmitted digital data. Apower connector 25 is coupled to a source of power from the systemplanar wiring 24 so as to provide the PAMM card 11 and associated memorydevices 13 and hub chip 15 with electrical power. Each ground connector23 may be coupled to a ground on the system planar.

Though not illustrated, each connector 17, 23, 25 on the bottom side ofPAMM card 11 has a corresponding coupling to a memory hub chip and/orDRAM chip on either the top of bottom side of the PAMM card 11. Eachcoupling facilitates connection to a pin or other attachment feature ofa memory device 13 or a hub chip 15, and hence, facilitates the transferof power and ground from the connectors 23, 25 to each memory device 13and signal, power and ground from the connectors 17, 23 and 25 to thehub chip 15. In one embodiment, the power connectors 25 and the groundconnectors 23 are alternated to provide isolation, as required, betweensignal pins 17.

As illustrated, the connectors 17, 23, 25 are preferably arranged in agrid formation comprised of rows and columns with the columns extendingin the direction of a centerline l extending along the length of thePAMM card 11. Each column of connectors is separated from adjacentcolumns of connectors by a column pitch p. Similarly, each row ofconnectors is separated from each adjacent row of connectors by a rowpitch r. Preferably, signal connectors 17, 17′ are arranged in pairs toform a multitude of differential wiring pairs 19.

Preferred ranges for column and row pitches p, r are limited by thestate of array connection technology and by signal density andmechanical loading requirements. In an embodiment, p and r range fromapproximately 0.5 mm to 3.0 mm. Such column and row pitches permit thesystem planar wiring 24 to reside on a single layer of the system planarusing lines and spaces (e.g., ˜100-micron line width and ˜100-micronspace width) suitable for high speed signaling and readily obtainablewith present circuit-card manufacturing techniques.

DIMM connectors are limited in their construction in that only one linecan be placed between pins. This limitation is restrictive to theincreasingly desired practice of using differential pair wiring forhigh-speed signals.

As noted above, signal connectors 17, 17′ are preferably arranged into amultitude of differential wiring pairs 19. There are illustrated inexemplary fashion two differential wiring pairs per channel. Sincehigh-speed wiring is usually differential, this is a preferredarrangement. Relaxation of the column and row pitch p, r may beperformed to a degree sufficient to reduce or practically eliminatenear-end cross talk (NEXT) and far-end cross talk (FEXT) so as toimprove IO performance. The power connectors 25 and ground connectors 23are preferably located along a center line l of the PAMM card 11 toprovide optimal power distribution. In addition, low power-planeinductance and minimal electrical crosstalk is achieved when the singleended wiring connections or the differential wiring pairs 19 areinter-digitated with additional power connectors 25 and/or groundconnectors 23.

The DRAM packages forming the memory devices 13 on each PAMM-card topview are illustrative only. Such memory devices 13 can be “bare die”attached, or preferably, small-sized packages such as “chip-scale”packages can be utilized. The size of the PAMM card 11 is illustrativeonly. In practice, a 50 mm×25 mm size PAMM card requires approximatelythe same amount of space on the system planer as a JEDEC standard 133 mmDIMM on 10 mm centers. In addition, if chip-scale packages are used, thedie can be easily pre-tested.

The particular embodiment shown in FIGS. 1 a and 1 b and 2 representsone of many possible physical form factors or electrical interfaceswhich may be employed. If more connectors are desired, they can be addedby extending the card length along center line l. Alternatively,connectors can be arranged closer together, either by changing the pitchbetween columns, rows, or both. Increasing the row pitch r providesincreased physical support to the PAMM card 11. As noted above, changingthe row pitch r from, for example, 2 mm to 1 mm, allows more rows to beadded for higher-capability PAMM (i.e. more pins and thus highercommunication bandwidth) without changing the fundamental pitch. Thatis, a high-speed test head designed to contact a 1 mm pitch PAMM canalso contact a 2 mm PAMM. Such an arrangement preserves investment intester cost, connector development, and the like.

Examples of alternative embodiments of the PAMM 10 illustratingdifferent connector configurations are shown in FIGS. 3-5. Withparticular reference to FIG. 5, the PAMM card 11 can be extended asneeded to accommodate multiple memory hubs 15 and associated DRAM memorydevices 13. In addition, memory devices 13 may be stacked as needed.

With reference to FIG. 6, there is illustrated a perspective view of anembodiment of a PAMM 10 coupled to a system planar 61. The system planarmay be, but need not be, composed of printed wiring board(PWB) material.Each illustrated PAMM 10 is formed of a single hub chip 15 and fivememory devices 13. Again, the number of memory devices illustrated isnot limiting as fewer or more devices can be accommodated. One will notethe generally planar nature of the PAMM 10 as it extends across anexpanse of the system planar 61 so that the major surfaces of the PAMM10 are generally parallel to those of the system planar 61. The PAMM 10can be soldered, or otherwise fastened, directly to the system planar61. Preferably, PAMM 10 is attached, or otherwise coupled, to the systemplanar 61 via a separable connector array 67 comprising a plurality ofconnectors 66 (not shown). The position of the separable connector array67 is indicated in FIG. 6 between the PAMM card 11 and the system planar61 but is not visible. Preferably, such a separable connector array 67is formed of a land-grid-array (LGA) interposer. or other grid styleconnector.

Typical LGA interposers require a retention hardware 68 to apply acompressive force between approximately 10 to 100 g per connector 66. Inthe embodiment illustrated, this force is provided through the provisionof PAMM attachment sites 63, 63′ located on opposing sides of the PAMMcard 11. PAMM attachment sites 63, 63′ are locations, preferably nearthe periphery of PAMM card 11, at which pressure may be applied tocouple the PAMM 10 to the system planar in an amount sufficient to meetthe per-connector force requirement. In a preferred embodiment, PAMMattachment sites 63, 63′ are formed of holes fabricated to receive anattachment device, such as a screw, for attaching the PAMM 10 to thesystem planar 61. Such screws 71 may include, but are not limited to, M3screws as shown in FIG. 7. In the embodiment shown, screws 71 operate inconcert with attachment sites 63 to form retention hardware 68.

Alternative methods for coupling the PAMM 10 to the system planar 61include hinge and latch systems and snap-in hold-downs that areengineered to provide both the required alignment of the connectors onthe bottom side of the PAMM 10 with associated contacts on the systemplanar wiring 24, and the retention hardware 68 to apply a compressiveforce and ensure a reliable connection. The separable connector 67 canbe completely separable from the PAMM 10 or system planar 61 and maycomprise a series of conduction bumps on a film or an array of metalsprings. Alternatively, the connectors on the bottom side of the PAMMcard 11 may be coupled to the system planar 61 either by moldingconductive contacts directly to either surface, or otherwise affixingspring contacts between the two.

With reference to FIG. 7, there is illustrated a heatsink 73 incombination with the PAMM 10. Heatsink 73 is formed of a base 77 and aplurality of fins 74. The base 77 is perforated by two or more holes 78through which screws 71 can pass. Heatsink 73 performs two functions.First, because heatsink 73 is coupled to the top surfaces of the memorydevices 13 and hub chips 15 through a thin layer 76 of thermal grease,glue, or other thermal-interface material that provides a low conductivethermal resistance, it operates to dissipate heat generated by thememory devices 13 and hub chips 15 by conducting the heat, through itsbase 77, to the large area of the heat-sink's fins 75, whence the heatis convected away by a stream of air or other fluid flowing through thechannels between the fins. Second, referring to the xyz coordinatesystem on FIG. 7, because the heatsink's fins 75 cause any cross sectionof the heatsink parallel to the xz plane to have a high area moment ofinertia, the heatsink 73 is very resistant to bending along the y axis,and thus very effective at transmitting the binding force of screws 71across the long y dimension of the PAMM 10, and functions as a keycomponent of the retention hardware 68 thereby insuring that each of theconnectors 66 in the connector array 67 receives the requiredcompressive force. Preferably, the conductive thermal resistance betweenthe heatsink base 77 and the heat-producing devices (hub chips 15 andthe memory devices 13) should be low. If the components 13, 15 aresubstantially co-planar, this is accomplished by a planar surface on theunderside of the heatsink base 77, because any small gaps betweenheatsink base 77 and heat-producing devices 13 and 15 can be effectivelyfilled by the thermal-interface layer 76. If however the components 13,15 are not substantially co-planar, a surface of heatsink base 77 inproximity to the top of PAMM 10 may be fabricated in negative reliefcorresponding to arrangement of the components 13, 15. As a result, athin memory device 13 possesses a correspondingly thicker area on theunderside of the heatsink base 77. Such a heatsink 73 may be machined,stamped, or cast.

With reference to FIG. 8, there is illustrated an embodiment of a PAMM10 wherein a screw-capturing device 85, such as an E-clip, is placedwithin a chip thickness space 81 extending from a surface of theheatsink 73 to a surface of the PAMM card 11. Capture device 85 capturesscrews 71 to heatsink 73 so that screws 71 are not easily lost whenheatsink 73 is removed.

With reference to FIG. 9 a, there is illustrated, in cross-section, anembodiment of a PAMM card 11. As illustrated, there is not a one to onecorrespondence between each coupling 91 and a single connector 17, 23,25. Internal connectors 93 may be arranged so as to couple the couplings91 to the connectors 17, 23, 25 in any desired configuration. Internalconnectors 93 form a part of PAMM card 11 and are constructed ofelectrically conductive material or wire. Note as well that the DRAMs 13may be coupled to the hub chip 15 via internal connectors 93 with thehub chip 15 coupled to one or more connectors 17, 23, 25 via internalconnectors 93. In addition, DRAMs 13 may be coupled to connectors 17,23, 25 without coupling to a hub chip 15.

With reference to FIG. 9 b, there is illustrated an embodiment of a PAMMcard 11 wherein DRAMs 13 are attached to both sides of PAMM card 11. Insuch a configuration, connector array 67 serves to provide a separationdistance 95 between the DRAMs 13 coupled to the lower side of PAMM card11 and the system planar 61. With reference to FIG. 10, there isillustrated a perspective view of the PAMM card 11 of FIG. 9 b makingclear the attachment configuration.

While there has been illustrated and described what is at presentconsidered to be a preferred embodiment of the claimed invention, itwill be appreciated that numerous changes and modifications are likelyto occur to those skilled in the art. In addition, the variousdimensions disclosed above, numbers of chips and the like are all to beviewed as exemplary, and not a limitation upon the use and practice ofthis invention. For example, the novel constructions shown in theFigures are not limited for use with memory chips and related circuits,but may be used as well with other circuit types. It is intended in theappended claims to cover all those changes and modifications that fallwithin the spirit and scope of the claimed invention.

1-16. (canceled)
 17. A method of making a circuit assembly comprising:providing a generally planar card comprising a first side and a secondside, said first side comprising a plurality of couplings and saidsecond side comprising a plurality of connectors; coupling a pluralityof memory devices to said card via a first portion of said plurality ofcouplings; coupling at least one hub chip to said card via a secondportion of said plurality of couplings; wherein each of said pluralityof couplings is connected to an associated one of said plurality ofconnectors.
 18. The method of claim 17 further comprising attaching saidcard to a system planar such that at least one of said plurality ofconnectors is coupled to a corresponding wire in a system planar wiring.19. The method of claim 17 further comprising the additional step ofinterposing a separable connector between said card and said systemplanar for coupling said plurality of connectors to said system planarwiring.
 20. The method of claim 19 wherein said separable connectorcomprises a LGA interposer.
 21. The method of claim 17 furthercomprising providing a heatsink having a heatsink base comprising asurface extending across said first side of said card.
 22. The method ofclaim 21 wherein said heatsink comprises a plurality of heat sink fins.23. The method of claim 22 wherein said heatsink fins are generallyaligned with an airflow direction.
 24. The method of claim 18 whereinsaid card is attached to said system planar through the use of anattachment device comprising at least one of pins, hinge and latchsystems, and snap-in hold-downs.
 25. The method of claim 17 wherein eachof said plurality of connectors is comprising at least one of powerconnectors, ground connectors, and signal connectors.
 26. The method ofclaim 17 wherein at least one of said plurality of memory devicescomprises a dynamic random access memory (DRAM) device. 27-33.(canceled)